2011 JK 3.8: I keep getting a consistent misfire (rough idle) on every cold startup that lasts for about a minute. Code 304 and 306. I also noticed the sound of air in the Heater core which made me think it was a faulty lower intake manifold gasket, but I still have the problem after changing the gasket. I already changed the Plugs, Wires, and Coil pack. Any ideas? Thanks!